Broad-band lumped-element circulator

ABSTRACT

A circulator preferably fabricated using thin film techniques. Broad-band isolation and insertion loss characteristics are obtained in the gigahertz frequency range by replacing the conventional series resonant circuit typically employed in circulation, with three symmetrically arranged lumped parameter LC circuits fabricated by thin-film techniques and having the junctions of the LC elements interconnected through conductive paths, such as inductors, for example.

United States Patent 1 1 Katoh [4 1 July 15, 1975 BROAD-BANDLUMPED-ELEMENT CIRCULATOR [75] Inventor: Hidehiko Katoh, Tokyo, Japan[731 Assignees Nippon Electric Company, Limited,

Tokyo, Japan 22 Filed: Mar. 6, 1974 21 Appl. No.: 448,556

[52] 0.8. CI. 333/11; 333/84 M [51] Int. Cl. HOlp 1/32 [58) Field ofSearch 333/l,l

[56] References Cited UNITED STATES PATENTS 3,522,555 8/1970 Hashimotoet al 333/l.l

3,818,38l 6/1974 Konishi et al 333/l.l

Primary ExaminerPaul L, Gensler Attorney, Agent, or F [rm-Ostrolenk,Faber, Gerb & Soffen [57] ABSTRACT A circulator preferably fabricatedusing thin film techniques. Broad-band isolation and insertion losscharacteristics are obtained in the gigahertz frequency range byreplacing the conventional series resonant circuit typically employed incirculation, with three symmetrically arranged lumped parameter LCcircuits fabricated by thin-film techniques and having the junctions ofthe LC elements interconnected through conductive paths, such asinductors, for example.

7 Claims, 9 Drawing Figures PATENTEDJIJL 1 5 ms 3 895, 320

sum 1 PRIOR ART l! SHEET ,LCENTRAL I CONDUCTOR I FERRITEL 1 24/ F l I I11' /I za/r 205 22f A 2635 22/ 2634 A I P PRIOR ART BROAD-BANDLUMPED-ELEMENT CIRCULATOR The present invention relates tolumped-element circulators. and more particularly to broad-bandlumpedelement circulators for applications at microwave frequencies. thecirculator being miniaturized by thin-film techniques used in thefabrication of integrated circuits.

BACKGROUND OF THE INVENTION With the constantly developing integrationof microwave circuits. there has been a growing demand for small.inexpensive circulators. Since an intermediate frequency of 1.7 GHz wasdetermined in Japan for millimeter wave PCM (pulse code modulation)communication systems, the need for circulators adaptable to highfrequency bands at this intermediate frequency has been on the rise.There have been several proposals on how to attain higher frequenciesand broader bands for circulators developed for VHF or UHF bands.

One proposal. made by R. H. Knerr of Bell Telephone Laboratories, Inc.at the International Microwave Symposium held in Dallas. Texas in May1969, suggests the use of thin-film techniques applied in thefabrication of semiconductor integrated circuits, to obtain highermicrowave frequencies for the circulator, The lumped-element circulatorused according to the proposal consists essentially of strip linescomprising several crossovers, which are formed on a ferrite disk. Thisapproach led to a marked increase in the upper limit of the frequency atwhich the circulator can operate. although a substantially wide band wasnot obtainable. To broaden the bandwidth, R. H. Knerr et al. proposed animprovement on the circulator to comprise capacitance formed bythin-film techniques, on the back of the ferrite disk, i.e., one of thetwo main surfaces of the ferrite disk where no strip lines are formed,(Reference: IEEE Transactions on Microwave Theory and Technique, VolMTT-l8, No. 12, December I970). According to this improvement. however,the specific bandwidth of the circulator is still insufficient; forexample. the ratio of the frequency band where an isolation of db can beobtained, to the center frequency is about percent at best.

Y. Konishi et al. proposed another improvement on the circulator usingan LC series circuit as a discrete element instead of the capacitanceformed on the back of the ferrite disk. This improvement. however, isnot very workable in broadening the bandwidth of a UHF band because. aswill be described, the single LC resonant circuit does not function as asymmetrical circuit on the back of the ferrite disk. (Reference: IEEETransactions on Microwave Theory and Technique, Vol. MTT-l9. No. 3,March 1971).

BRIEF DESCRIPTION OF THE INVENTION AND OBJECTS Studying the prior artapproaches, the inventors of the present invention found the fact thatthe microwave frequency bandwidth can be broadened by splitting KonishisLC series circuit into three components as in the microwave stripcircuit on the top surface of the ferrite disk and by forming thesecomponents into a distributed constant circuit by thin-film techniques.(Ret erence: Rec. Professional Group on Microwaves, No. MW 72-89. Oct.26. 1972, issued by The Institute of Electronics and CommunicationEngineers of Japan). This improvement served to increase the specificbandwidth to a value higher than 40 percent. On the other hand, however.a complex series resonant circuit is formed among the three-component LCseries circuits on the back of the ferrite disk. as will he describedlater. causing the isolation and insertion loss characteristics to belargely deformed within the frequency band used.

Accordingly, a general object of the invention is to provide a microwaveband lumped-element circulator miniaturized by the use of thin-filmtechniques and made operable over a broader microwave frequency band andexhibiting flat isolation and insertion loss characteristics.

BRIEF DESCRIPTION OF THE FIGURES The other objects, features andadvantages of the invention will become more apparent from the followingdescription taken in conjunction with the accompanying drawings wherein:

FIG. I is a perspective view showing the conventional lumped-elementcirculator proposed by Konishi et al..

FIG. 2 is a bottom plan view showing a ferrite disk of the circulator asin FIG. 1, proposed by the inventors,

FIG. 3 is an equivalent circuit diagram of a threecomponent LC seriesresonant circuit formed on the back of the ferrite disk shown in FIG. 2,

FIG. 4 is an equivalent circuit diagram similar to FIG. 3., showing anembodiment of the invention. which comprises a means for precluding theproblems attendant on the prior art illustrated in FIG. 3,

FIG. 5 is a bottom plan view similar to FIG. 2. corresponding to theequivalent circuit shown in FIG. 4,

FIG. 6 is a diagram showing isolation/insertion losses vs. frequencycharacteristics for illustrating the effects of the invention,

FIG. 7 is a longitudinal sectional view showing the ferrite disk as inFIG. 5 mounted in a housing.

FIG. 8 is a longitudinal sectional view showing another example offerrite disk mounted in a housing, and

FIG. 9 is a plan view showing a ferrite disk on which three input armsare installed, each comprising an LC series circuit, for the purpose ofbroadening the frequency band used.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. I, there isshown one conventional circulator proposed by Konishi et al., whichcomprises a ferromagnetic ferrite substrate 10; a center conductorelement 11 formed on the top surface of the substrate 10 by way ofazero-capacitance-insulated crossover and having three arms I20 apartfrom each other; an outer conductor element 12 formed on the entire backsurface of the substrate; thin-film strips 13 con necting the three armsat every other end to the outer conductor element 12; input/outputterminals 14A, 14B and 14C each respectively connected to one of thethree arms on the side opposite to the thin-film strips 13; shuntingcapacitors 15A, 15B and 15C for shunting the input/output terminals tothe outer conductor element I2; and a series resonant circuit 16inserted in seties between the outer conductor element 12 and the groundE. The resonant circuit 16 comprises such lumped-constant circuitelements as an inductor 161 and a capacitor 162. The aim of thiscirculator is to achieve wide-banding effects by utilizing the shuntingcapacitors 15A through 15C of the individual input- /output ports, incombination with the series resonant circuit 16. However. because theinductor I6! is included in the single resonant circuit 16 there aredifficulties in symmetrically maintaining the isolation characteristicand the insertion loss characteristic in the UHF region above I GHz.Accordingly the upper limit of the usable frequency remainscomparatively low. For example. in the 1 GHz region. the specific bandof a frequency region where the symmetry of the characteristics can beobtained is as low as about l3 percent.

The reason why the upper limit of the frequency range is low in thecirculator proposed by Konishi et al. is because the discrete inductor161 of the series resonant circuit I6 adversely affects the symmetry ofthe circulator. To solve this problem. the inventors of this inventionproposed the arrangement that the inductor I61, together with thecapacitor 162, is split into three components. which are installed onthe back main surface of the ferrite substrate 10. surrounding the outerconductor element 12 (Reference is made to the foregoing data issued byThe Institute of Electronics and Communication Engineers of Japan). FIG.2 briefly illustrates by bottom plan view the essential part on theferrite substrate used for the purpose of the invention.

In FIG. 2. an LC series broad-banding circuit formed on the back mainsurface of a ferrite substrate by thin-film techniques comprises: acircular main conductor film 22 connected by way of three throughholes HH; and H;, to three arms (which correspond to three arms of centerconductor 11 in FIG. 1) of the center conductor on the top main surfaceof the ferrite substrate 20. a substantially annular shaped groundingconductor film 22E surrounding center conductor 22 and being spacedtherefrom by a predetermined distance d from the circumference of mainconductor film 22, concentrically arranged inductive arms 261A, 26IB and261C formed integrally with the conductor film 22 in the same process inan exposed region 22F of the width d between the conductor film 22 andthe grounding conductor film 22E; and interleaved finger capacitiveelement portions 262A. 2628 and 262C linked with the grounding conductorfilm 22E at the ends of inductive arms 261A. 2618 and 261C. Theseinductive and capacitive arms 261A through 261C and 262A through 262Care arranged at I20 intervals relative to one another when viewed fromthe center of the conductor film 22. The arms 261A through 261C and 262Athrough 262C are formed concurrently with the conductor films 22 and 22Ein a thin-film forming process.

FIG. 3 shows an equivalent circuit of the outer con ductor arrangementwherein three series resonant circuits 26lA-262A. 26IB262B and 26IC-262Care inserted between the main conductor film 22 and the groundingconductor film 22E. As apparent from the equivalent circuit. there arethree complex series resonant circuits formed at the same time. that is,a first complex series resonant circuit I comprising 26IA-26-2A-262B-261B, a second complex series resonant circuit I Comprising26lB-262B-262C-26IC, and a third complex series resonant circuit Icomprising 261A- 262A-262C-261C. In this construction. however. aparasitic resonant circuit is formed. with the result that flatisolation and insertion loss characteristics can hardly be obtained bymerely depending on the circuits shown in FIGS. 2 and 3.

As a result of studying possibilities of reducing the effect of theparasitic resonant circuit. the inventors of this invention have foundan effective arrangement as indicated by an equivalent circuit shown inFIG. 4. This arrangement is such that the LC connection points of theseries resonant circuits 261A-262A. 2613-2628 and 26IC-262C are shuntedby inductors 263A. 2635 and 263C respectively. By giving the inductancesof these inductors as small values as possible (the inductance value canbe nearly zero under a shortcircuit state the effect of the parasiticresonant circuit can be substantially removed.

FIG. 5 is a bottom plan view of a ferrite substrate 20 as in FIG. 2,which is embodied from the equivalent circuit in FIG. 4 by the use ofthin-film techniques. In FIG. 5, the connection points of inductor arms261A. 261B and 261C. and capacitor arms 262A, 2628 and 262C are shuntedby inductive shunting elements 263A. 2638 and 263C respectively. It isapparent to those skilled in the art that these conductor thin-filmelements are formed concurrently in one process by the known thin-filmtechniques.

FIG. 6 shows isolation and insertion losses vs. frequencycharacteristics according to the invention, in comparison with the priorart characteristics. In FIG. 6, the abscissa stands for frequencies ingigahertz (GI-I2), the ordinate for isolation and insertion losses indecibel (db). the solid line for the characteristic of the embodiment asin FIG. 5, and the dotted line for the characteristic according to theprior art as in FIG. 2. FIG. 6 indicates the fact that the prior artcharacteristic curve is largely varied in the frequency band used. asopposed to a flat curve obtained according to the invention.

FIG. 7 is a sectional view of the embodiment of FIG. 5 taken across thedot-dash line 7 away from the arrowmarked direction, showing theconstruction ofa practical circulator mounted in a housing. Thiscirculator comprises a ferrite substrate 20 having a thin-film outerconductor arrangement (FIG. 5). In FIG. 7, the ferrite substrate 20 isfitted to a conductor housing member 30 on the grounding conductor film22E. This ferrite substrate 20, on the other hand, is connected to acenter conductor 32 of a connector 31 (which is to serve as aninput/output terminal) on the surface where a central conductor 11 isformed. The housing member 30 and the connector 31 are integrally unitedby soldering or the like along their mating surfaces. To operate thiscirculator, a static magnetic field is applied in the directionindicated by arrow M. The ferrite substrate 20 is mounted in the housingmember 30 in the manner well-known to those skilled in the art, whichtherefore is not described further for purposes of simplicity.

In the first embodiment of the invention shown in FIG. 5, the conductorthin film pattern which is one element characterizing this invention. isformed directly on the back surface of the ferrite substrate 20. Thisthin-film pattern may be formed on a suitable substrate such as ceramicsubstrate if the circulator is required to be related to an externalcircuit. An example of this construction is illustrated by a sectionalview shown in FIG. 8. Like references denote like components throughoutFIGS. 2, 7 and 8, and references with primes in FIG. 8 indicatecomponents corresponding to those in FIGS. 2 and 7. In FIG. 8, athin-film circuit patcm as shown in FIG. 5; which uniquely characterizesthis invention, is formed on the back surface of 3. ccramic substrate40. A metallized portion 41 is formed on the top surface of the ceramicsubstrate 40. A conductive film I2 is formed on the entire surface ofthe bottom of the ferrite substrate 20, which is then installed on themetallized portion 41 by soldering or the like. In this process, anaxial through-hole may be formed at the center of the ceramic substrate.through which the conductor films l2 and 22 are electrically connectedto each other. One end of each arm of the central conductor is connectedto the conductive film 12' by a shunt conductor 13'. and theinput/output terminal of each arm is led through a conductor strip 42 toan electrode member 43 on the ceramic surface and is then connected tothe central conductor of the connector 31. To operate this circulator. astatic magnetic field M is applied in the upward direction perpendicularto the plane of drawing.

According to the invention, as described above, the frequency bandapplicable to the circulator is broad ened by controlling the conductorthin-film pattern of the outer conductor formed on the side opposite tothe central conductor of three arms. The band-broadening effect can beenhanced when the conventional broadbanding method in which LC seriesresonant circuits are connected in series to the individual input/outputports is used with the circulator construction of this invention. FIG. 9shows by plan view an example of the shape of central conductor 11 usedfor this arrangement. In FIG. 9, series resonant circuits as shown inFIGS. 2 and 5 are formed between the three arms of central conductor 11with shunting capacitors 15A, 15B, 15C 15 and the input/output ports14A, 14B and 14C (note: The method of broadening the band by the use ofseries resonant circuits in the input/output ports as is described inthe foregoing proposal by R. H. Knerr. Hence, no further descriptionthereof will be given herein). Alternatively, the series resonantcircuits may be formed on a ceramic plate, which may be stacked with theferrite plate to permit those resonant circuits to surround the centerconductor.

According to the invention, as has been described in detail, the LCseries circuit of the outer conductor is split into three components,the connection points of the three-component series resonant circuitsare shunted by inductors, and these circuit elements are formed bythin-film techniques whereby a circulator operator at a higher frequencyand in a broader frequency band is realized.

While a preferred embodiment of the invention and several modificationsthereof have been described, it is particularly understood that theinvention is not limited thereto or thereby.

What is claimed is:

1. A broad-band thin-film circulator having a plate of ferromagneticmaterial, means creating a DC. magnetic field transverse to said plate,at least three arms of mutually insulated thin conductor films formed onone major surface of said plate, terminal members connected respectivelyto one end of each of said arms; a centrally located conductive filmformed on the oppo site surface of said plate; means connectedrespectively to said conductor films for electrically connecting theother ends of said conductor film arms to said central conductive filmand including resonant means including LC circuit elements and connectedat one end to said central film and electrostatically coupled at theopposite end with the other ends of said conductive film arms, whereinsaid resonant means comprises three LC series circuit paths eachcomprising an inductor and capacitor; conductive elements connectingeach junction between an inductor and capacitor to every otherjunction,

2. A circulator as claimed in claim 1, wherein said LC series circuitelements are formed of symmetrical thin film conductor patterns formedon the other major surface of said plate,

3. A circulator as claimed in claim 1, wherein said LC series circuitelements are formed on a major surface of a ceramic plate separate fromsaid ferrite plate and coupled with said ferrite plate.

4. A circulator comprising a substantially disc-shaped body offerromagnetic material;

means creating a DC. magnetic field transverse to said body;

a thin-film conductive pattern formed on one face of said body saidpattern comprising three conductive arms arranged at predetermined equalangles relative to one another;

a circular shaped conductive thin-film formed on the opposite face ofsaid body;

means connecting one end of each arm to said circular-shaped thin-film;

an annular conductive thin-film formed on said opposite face andsurrounding said circular shaped thinfilm. the thin-films defining anannular space therebetween;

a plurality of thin-film LC circuit paths arranged at predeterminedlocations within said annular space, each path containing first andsecond lumped parameter circuit elements joined to one another;

one end terminal of each circuit path being connected to said circularthin-film and the opposite end terminal of each circuit path beingconnected to said annular shaped thin-film;

a thin-film conductive pattern formed in said annular space forelectrically interconnecting the junctions between the first and secondlumped parameter elements of each of said series circuits.

5. The circulator of claim 4 wherein said thin-film conductive patternin said annular space comprises a plurality of inductors each of saidinductors being connected between the junctions of a pair of saidcircuit paths.

6. The circulator of claim 5 wherein first, second and third seriescircuit paths are provided and are arranged at equi-spaced intervalsabout said annular space;

said plurality of inductors comprising first, second and third inductorsarranged at equi-spaced intervals about said annular space and eachbeing electrically connected between the junctions of two associatedones of said series circuit paths.

7. The circulator of claim 6 wherein each of said series circuit pathscomprises series connected inductance and capacitance elements.

1. A broad-band thin-film circulator having a plate of ferromagnetic material, means creating a D.C. magnetic field transverse to said plate, at least three arms of mutually insulated thin conductor films formed on one major surface of said plate, terminal members connected respectively to one end of each of said arms; a centrally located conductive film formed on the opposite surface of said plate; means connected respectively to said conductor films for electrically connecting the other ends of said conductor film arms to said central conductive film and including resonant means including LC circuit elements and connected at one end to said central film and electrostatically coupled at the opposite end with the other ends of said conductive film arms, wherein said resonant means comprises three LC series circuit paths each comprising an inductor and capacitor; conductive elements connecting each junction between an inductor and capacitor to every other junction.
 2. A circulator as claimed in claim 1, wherein said LC series circuit elements are formed of symmetrical thin film conductor patterns formed on the other major surface of said plate.
 3. A circulator as claimed in claim 1, wherein said LC series circuit elements are formed on a major surface of a ceramic plate separate from said ferrite plate and coupled with said ferrite plate.
 4. A circulator comprising a substantially disc-shaped body of ferromagnetic material; means creating a D.C. magnetic field transverse to said body; a thin-film conductive pattern formed on one face of said body said pattern comprising three conductive arms arranged at predetermined equal angles relative to one another; a circular shaped conductive thin-film formed on the opposite face of said body; means connecting one end of each arm to said circular-shaped thin-film; an annular conductive thin-film formed on said opposite face and surrounding said circular shaped thin-film, the thin-films defining an annular space therebetween; a plurality of thin-film LC circuit paths arranged at predetermined locations within said annular space, each path containing first and second lumped parameter circuit elements joined to one another; one end terminal of each circuit path being connected to said circular thin-film and the opposite end terminal of each circuit path being connected to said annular shaped thin-film; a thin-film conductive pattern formed in said annular space for electricallY interconnecting the junctions between the first and second lumped parameter elements of each of said series circuits.
 5. The circulator of claim 4 wherein said thin-film conductive pattern in said annular space comprises a plurality of inductors each of said inductors being connected between the junctions of a pair of said circuit paths.
 6. The circulator of claim 5 wherein first, second and third series circuit paths are provided and are arranged at equi-spaced intervals about said annular space; said plurality of inductors comprising first, second and third inductors arranged at equi-spaced intervals about said annular space and each being electrically connected between the junctions of two associated ones of said series circuit paths.
 7. The circulator of claim 6 wherein each of said series circuit paths comprises series connected inductance and capacitance elements. 